1. Field of the Invention
The present invention relates to a technique of displaying an analysis image of a target region such as an angiostenosis part with an X-ray image being taken.
2. Description of the Related Art
Conventionally, there has been a treatment technique such that a linear structure such as a guide wire or a catheter is inserted into coronary arteries of a heart to expand a portion where the coronary arteries are narrow or blocked. This treatment technique is referred to as “Percutaneous Coronary Intervention (PCI) treatment”. In the PCI treatment, an X-ray imaging apparatus such as an X-ray angiography apparatus is used. The X-ray angiography apparatus displays an X-ray perspective projection image (hereinafter, “X-ray angiographic image”) as a guide image at the time of inserting a guide wire up to a lesioned part (a coronary artery stenosis site) during the PCI treatment.
Further, as means for diagnosing coronary arteries, clinical application software for an X-ray CT scanner referred to as “coronary artery analysis software” has been known (for example, see JP-A 2004-283373 (KOKAI)). This coronary artery analysis software has a function for obtaining a blood vessel core of the coronary arteries, an internal wall of a blood vessel, an estimated normal internal wall of a blood vessel, and the like as three-dimensional data using three-dimensional volume data of a heart area.
In PCI treatment, therefore, images of the internal wall of a blood vessel obtained by the coronary artery analysis software are displayed on an another apparatus separate from an X-ray angiography apparatus or developed on a film for reference, to support an operator.
Further, a technique for synthesizing and displaying analysis images showing an angiostenosis part and a running direction of a blood vessel obtained by coronary artery analysis software on an X-ray angiographic image has been developed. To generate the analysis images of the angiostenosis part and the running direction of a blood vessel, projection parameters (projection directions, positions, and enlargement ratios) need to be obtained. To obtain these projection parameters, therefore, a positioning process is performed in a following procedure.
(1) First, to match a projection direction, a user manually sets so that a projection direction of volume data becomes the same as that of the X-ray angiography apparatus.
(2) The volume data is projected from the direction set in procedure (1) to generate an MIP image, and the maximum intensity projection (MIP) image is binarized to an imaged blood area and other areas.
(3) An image showing only the blood area imaged by binarization is generated from the X-ray angiographic image.
(4) To perform positioning between binarized image f1(x, y) in procedure (2) and binarized image f2(x, y) in procedure (3), a parallel shifting amount (l, m) and an expansion ratio s are obtained by a correlation function shown in an equation (1).
                              r          ⁡                      (                          l              ,              m              ,              s                        )                          =                              1                          N              2                                ⁢                                    ∑                              x                =                                                      -                    N                                    /                  2                                                                              N                  /                  2                                -                1                                      ⁢                                          ∑                                  y                  =                                                            -                      N                                        /                    2                                                                                        N                    /                    2                                    -                  1                                            ⁢                                                                    f                    1                                    ⁡                                      (                                          x                      ,                      y                                        )                                                  ·                                                      f                    2                                    ⁡                                      (                                                                                            (                                                      x                            +                            l                                                    )                                                /                        s                                            ,                                                                        (                                                      y                            +                            m                                                    )                                                /                        s                                                              )                                                                                                          (        1        )            
However, in the positioning process mentioned above, entire processing is performed after imaging by the X-ray angiography apparatus has started, and thus a longer processing time is required. During PCI treatment, an operator performs surgery, while appropriately changing the imaging direction and position of the X-ray angiography apparatus so that an observation target can be clearly seen on the displayed image. Therefore, every time the imaging direction of the X-ray angiography apparatus is changed, the positioning process needs to be performed from procedure (1), and thus the waiting time for positioning is required. As a result, the surgery time becomes longer, and strains on the patient increase.